This invention relates to an image forming apparatus with a forming position correcting function and, more particularly, to an image forming apparatus suitable for an electronic copying machine in which, when two sets of image forming procedures are conducted to form a final image on a same sheet of image receiving medium, any discrepancies concerning positioning of the image between said two sets of procedures are eliminated by a forming position correcting function.
A conventional copying machine having a function of forming an image on both sides of a sheet of copying paper and a copying machine having a function of forming multiple images on a single sheet of copying paper as well as a copying machine having these two functions are already known.
In any of the aforementioned types of copying machines, a single sheet of copying paper is moved back to the copying post after completion of a first set of image forming procedures to undergo a second set of image forming procedures. If, in such a type of machine, a sheet of copying paper is to travel a long way for a second set of copying procedures or it is temporarily stored in a paper stack section on its way back to the copying post, it can be diverted longitudinally and/or laterally so that it may come back to the same position as it was located when it underwent the first set of copying procedures. Such positional discrepancies can adversely affect the quality of the final image particularly when multiple sets of image forming procedures are conducted on a same sheet of copying paper.
In a copying machine, in which two developing units are incorporated for two different colors, black and red for example, a sheet of copying paper is fed to a first developing unit, for black color for example, for the first set of copying procedures and then to a second developing unit for the second set of copying procedures.
In this type of copying machine, any positional deviation, longitudinal and/or lateral, at the first copying post can be carried over to the second copying post without any corrective measures, causing a blurred or smeared final image in most cases.